Swedish activist Greta Thunberg was arrested Tuesday under terrorism laws in Britain for holding a placard that the police said showed support for the banned group Palestine Action, her lawyer and organizers of the protest said.

Thunberg, 22, joined a protest in London’s financial district Tuesday morning that opposed the treatment of people being held in prisons before trials relating to Palestine Action activities, most for property damage at Israel-linked weapon firms. Several of those being held have gone on hunger strike.

Video released by the protest organizers, a separate group called Prisoners for Palestine, showed Thunberg sitting on a sidewalk holding a handwritten sign reading, “I support Palestine Action prisoners. I oppose genocide.” The video shows a police officer asking her to stand up and taking the sign. As protesters shout “Free, free Palestine,” a person is heard heckling off camera, saying, “Take the terrorist away.”

In a statement, the City of London Police said that a 22-year-old woman had been arrested “for displaying an item (in this case a placard) in support of a proscribed organization (in this case Palestine Action) contrary to Section 13 of the Terrorism Act 2000.” The statement did not name Thunberg, in accordance with rules barring British police from identifying suspects before they are charged.

The police later said that the woman had been released on bail and asked to return in March.

In a statement, Raj Chada, a lawyer representing Thunberg, said: “Our client has been arrested under the U.K.’s farcical terror laws. The U.K.’s global reputation for human rights is in tatters whilst these laws remain in place.”

Thunberg was arrested under a law that has been used to arrest more than 2,000 people since Palestine Action was banned as a terrorist group in July. The law makes it a crime to wear, carry or display items that “arouse reasonable suspicion” of support for banned organizations and can be punished with up to six months in prison. Most of the arrests have been for holding signs with the phrase “I oppose genocide. I support Palestine Action.”

Palestine Action is the first organization to have been declared a terrorist group under part of Britain’s legal definition of terrorism that covers “serious damage to property” for a political cause, rather than violence against people.

The Palestine Action ban is being challenged by its co-founder at the High Court in London as unlawful and disproportionate.

The group had used property damage, particularly spraying red paint, as a tactic in protests that mainly targeted subsidiaries of Israeli weapon manufacturer Elbit Systems and other companies that the group accused of links to the Gaza conflict.

Tuesday’s protest was held outside the offices of an insurance company in London. Protest organizers said the company had provided services to Elbit Systems U.K.

In a statement, the City of London Police said the demonstration started about 7 a.m. Tuesday, when protesters used hammers and red paint to damage the building. Aside from Thunberg, a man and a woman were arrested on suspicion of criminal damage.